JPH0321108A - Crystal oscillator circuit - Google Patents

Abstract

PURPOSE:To obtain an inverter type crystal oscillator circuit in which the oscillation frequency to temperature change is a smooth n-th order curve by providing the circuit with a crystal oscillator, 1st and 2nd inverters, 1st and 2nd fixed resistors and 1st and 2nd capacity elements. CONSTITUTION:The crystal oscillator circuit is constituted of the crystal oscillator 1, the inverters I1, I2, the capacitor elements C1, C2, and the fixed resistors R1, R01. In said constitution, the inverter I1 acts as an inversion amplifier and the fixed resistor R1 forms a feedback circuit. The oscillation frequency of the circuit is determined by the crystal oscillator 1, the variable capacity element Cv and the capacity elements C1, C2. When the fixed resistor R01 is inserted between the variable capacity element Cv connected to the oscillator and the inverter I1, the oscillation level of the oscillator 1 is dropped and the n-th order curve of which frequencytemperature characteristic is smooth can be obtained.

Description

[Detailed Description of the Invention] [Summary] Regarding the inverter type crystal oscillator circuit used in a digitally controlled temperature compensated crystal oscillator, the present invention provides an inverter type crystal oscillator circuit in which the change in oscillation frequency with respect to temperature change is a smooth n-th order curve. A first inhertor for oscillation, a first fixed resistor connected in parallel to the input and output terminals of the first inherter, and one end of which is connected to the lth inherter.
a crystal resonator connected to the input end of the inverter, the other end of which is connected to one end of a variable capacitance element that finely adjusts the oscillation frequency, and a first capacitor connected between the input end of the first inverter and the ground. a second capacitive element that connects the other end of the variable capacitive element and ground, a second inverter for output that is connected to the output end of the first inverter, and an output end of the first inverter. and the other end of the variable capacitance element.

[Industrial application field]

The present invention relates to an inverter type crystal oscillation circuit used in a digitally controlled temperature compensated crystal oscillator.

For example, oscillators used in frequency sources such as mobile radio equipment are required to have particularly high accuracy, so digitally controlled temperature-compensated crystal oscillators (hereinafter referred to as DTCX○), which digitally compensate for temperature characteristics, are required. , is becoming widely used.

In order to accurately perform temperature compensation of the DTCXO, it is necessary that the frequency-temperature characteristic of the crystal oscillation circuit before temperature compensation be a smooth n-th order curve.

[Conventional technology]

FIG. 5 is a diagram for explaining the conventional example, and FIG. 6 is a diagram for explaining the frequency-temperature characteristic of the conventional example.

In the conventional example shown in FIG. 5, the first inverter for oscillation ■1
, a first fixed resistor RL connected in parallel to the human output terminal of the first inverter, and a variable crystal oscillator 1 connected in parallel to the human output terminal of the first inverter. a series circuit of capacitive elements Cv; a first capacitive element CI connecting between the input end of the first inverter I1 and the ground; a second capacitive element C2 connecting the output end of the first inverter I1 and the ground; The second inverter I2 for output is connected to the output end of the first inverter X1.

In this circuit, the inverter II operates as an inverting amplifier, the first fixed resistor R1 acts as a feedback resistor, and the crystal oscillator 1, variable capacitor Cv, first capacitor CI, and second capacitor The oscillation frequency is determined by the capacitive element C2.

Figure 6 shows the inverter type crystal oscillator 3 with the configuration shown in Figure 5. 4 This is the frequency-temperature characteristic of the circuit.

The temperature characteristics of a crystal resonator generally have a smooth curve, but the temperature characteristics of a conventional inverter type crystal oscillation circuit do not have a smooth curve as shown in FIG.

[Problem to be solved by the invention]

In the conventional example described above, since the excitation level of the crystal resonator l is high, the frequency-temperature characteristic of the inverter type crystal oscillation circuit has severe irregularities as shown in FIG.

In order to compensate for temperature characteristics, the DTCXO maintains high frequency stability by measuring the temperature at which the crystal oscillation circuit is placed and controlling it by applying a digital control signal according to the temperature. In the case of frequency-temperature characteristics as shown in FIG. 6, it is necessary to create temperature compensation data in fine temperature steps.

SUMMARY OF THE INVENTION An object of the present invention is to provide an inverter type oscillation circuit in which the oscillation frequency changes smoothly to the n-th +th line with respect to temperature changes.

[Means to solve the problem]

FIG. 1 is a diagram illustrating an embodiment of the present invention.

In the embodiment of FIG. 1, I1 is the first inverter for oscillation, Rl is the first fixed resistor connected in parallel to the input and output terminals of I1, and 1 is the first fixed resistor. A crystal oscillator that determines the oscillation frequency together with Cv is connected to the input end of the inverter 11, and the other end is connected to one end of the variable capacitance element Cv, and Cl is connected between the input end of the first inverter I1 and the ground. C2 is the first capacitive element that connects the other end of the variable capacitive element Cv and the ground.
I2 is a second inverter for output connected to the output end of the first inverter I1, and ROI is the output end of the first inverter I1 and the other end of the variable capacitance element Cv. There is a second fixed 5 6 1 resistor that connects between the two, and providing such a means is a means for solving this problem.

(Function) In the above-described circuit, the first inverter I1 operates as an inverting amplifier for oscillation, and R1 is a fixed resistor for feedback.

The oscillation frequency of this circuit is determined by the crystal resonator 1, the variable capacitive element Cv, the first capacitive element C1, and the second capacitive element C2.

At this time, a fixed resistor RO is connected between the variable capacitance element Cv connected to the crystal resonator 1 and the first inverter I1.
By inserting I, it is possible to lower the excitation level of the crystal oscillation and obtain an n-th order curve with smooth frequency-temperature characteristics.

[Examples] The gist of the present invention will be explained in detail below with reference to Examples shown in FIGS. 1 to 4.

FIG. 1 is a diagram for explaining an embodiment of the present invention, FIG. 2 is a diagram for explaining other embodiments of the present invention, FIG. 3 is a diagram for explaining frequency-temperature characteristics of a length embodiment of the present invention, and FIG. The figures each show a diagram illustrating a digitally controlled temperature compensated crystal oscillator. Note that the same reference numerals indicate the same objects throughout the figures.

In the embodiment of the invention shown in FIG. 1, the excitation level of the crystal resonator 1 is adjusted by inserting a fixed resistor ROI between the output terminal of the first inverter I1 for oscillation and the variable capacitance element Cv. It becomes possible to obtain an inverter-type crystal oscillation circuit with a smooth nth-order curve in frequency-temperature characteristics.

In another embodiment shown in FIG. 2, the basic structure of the inverter-type crystal oscillator circuit is the same as that in the embodiment shown in FIG. RO2 is inserted between the crystal resonator 1 and the variable capacitance element Cv.

Figure 3 is composed of crystal oscillations as shown in Figures 1 and 2.
FIG. 78 is a diagram illustrating the frequency-temperature characteristics of an inverter-type crystal oscillation circuit with a lower excitation level of -1, and a smooth nth-order curve can be drawn.

FIG. 4 is a diagram illustrating a digitally controlled temperature compensated crystal oscillator, in which temperature is measured by a temperature sensor, the result is A/D converted by an A/D conversion circuit 20, and sent to a control circuit 30. input.

The control circuit 30 reads out the compensation value determined from the received temperature information from the compensation table, and reads the compensation value determined from the received temperature information,
The D/A conversion circuit 40 performs temperature compensation by D/A converting the received compensation value and inputting it as an analog control voltage to the crystal oscillation circuit 50.

The control circuit 30 has a table containing compensation values for each temperature, and such a compensation table is created by taking frequency-temperature characteristic data for each oscillator in advance.

By using a crystal oscillator circuit whose frequency-temperature characteristic has a smooth nth-order curve as in the present invention, it becomes easy to create a temperature compensation table and it is possible to improve the compensation accuracy.

〔Effect of the invention〕

According to the present invention as described above, by lowering the excitation level of the crystal resonator, it is possible to provide an inverter-type crystal oscillation circuit whose frequency-temperature characteristics have a smooth nth-order curve.

[Brief explanation of the drawing]

FIG. 1 is a diagram for explaining an embodiment of the present invention, FIG. 2 is a diagram for explaining another embodiment of the present invention, FIG. 3 is a diagram for explaining frequency-temperature characteristics of an embodiment of the present invention, FIG. 4 is a diagram for explaining a digitally controlled temperature compensated crystal oscillator, FIG. 5 is a diagram for explaining a conventional example, and FIG. 6 is a diagram for explaining the frequency-temperature characteristic of the conventional example. In the figure, ■ is a crystal oscillator, I1 and I2 are interconnectors, C1 and C2 are capacitive elements, 9 10 Cv is a variable capacitive element, R1, ROI, and RO2 are fixed resistors, 10 is a temperature sensor, and 20 is an A/ 30 is a control circuit; 40 is a D/A conversion circuit; and 50 is a crystal oscillation circuit. -11 Figure 2 for explaining other embodiments of the present invention Figure 1 for explaining embodiments of the present invention Figure 4 for explaining a digitally controlled salinity compensated crystal oscillator Figure 5 to explain

Claims (1)

[Claims] An inverter-type crystal oscillation circuit used in a digitally controlled temperature-compensated crystal oscillator, comprising a first inverter (I1) for oscillation and an input/output terminal of the first inverter (I1) in parallel. one end is connected to the input end of the first inverter (I1), and the other end is one end of a variable capacitance element (Cv) that finely adjusts the oscillation frequency. a crystal resonator (1) connected to the first inverter (I1), a first capacitive element (C1) connecting the input end of the first inverter (I1) to the ground, and the other end of the variable capacitive element (Cv). a second capacitive element (C2) connected to the ground; a second output inverter (I2) connected to the output end of the first inverter (I1); and the first inverter (I1). A crystal oscillation circuit comprising a second fixed resistor (R01) connecting between the output end of the variable capacitance element (Cv) and the other end of the variable capacitance element (Cv).